1. Field of the Invention
The present invention relates to an image processing apparatus for suppressing deterioration of an image at the time of enlargement or reduction.
2. Description of the Related Art
In a conventional image processing apparatus which scans an image with an image input device and provides a hard copy or the like of the image after subjecting the image to enlargement/reduction processing, the response of a high-frequency component is impaired due to the response of a scanning lens and the size of the sensor opening, providing a blurred output image. In addition, the output image is often blurred due to not only a reduction in the response in the image input device but also the algorithm for the enlargement/reduction processing. Particularly, when an enlargement ratio is increased, it is difficult to suppress blurring using any algorithm for enlargement/reduction processing, so that the edge of a character image or the like is blurred, making it significantly awkward. There is a technique known which combines enlargement/reduction processing and high-frequency area emphasis for emphasizing the high-frequency component to suppress the reduction in the response of the high-frequency component, thereby preventing generation of enlargement/reduction-originated blurring (see Published Unexamined Japanese Patent Application No. 62-257276).
However, the high-frequency area emphasis may rather make an image awkward, depending on images. For instance, when a dot image is expanded, its dot pattern is easily seen, and when the high-frequency component of the image is emphasized, the dot pattern alone becomes prominent, making it difficult to identify the original image. Further, reduction of a dot pattern is likely to be a cause for moire noise.
Even emphasizing the high-frequency component of an image after enlargement of the image does not provide good effect to suppress image deterioration. If image reduction is done after the high-frequency component of the image is emphasized, not only the moire noise is generated but the reproduced image would have many rough portions.
As described above, with the use of the prior art image processing apparatus which compensates for reduction in high spatial frequency caused by enlargement/reduction processing to uniformly emphasize the high-frequency component, an awkward cyclic pattern or moire noise is rather emphasized, or the desired rich effect cannot be obtained, depending on the type of images.